Grease composition for use in constant velocity joints comprising at least two different molybdenum compounds

ABSTRACT

In order to provide for a grease composition reducing or preventing noise, vibration and harshness (NVH) in the driveline, a grease composition for use in constant velocity joints is suggested, comprising a) a base oil composition; b) at least one tri-nuclear molybdenum compound of the formula MO 3 S k L n Q Z , wherein L are independently selected ligands having organo groups with a sufficient number of carbon atoms to render the compound soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 though 7, Q is selected from the group of neutral electron donating compounds such as amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values. c) at least one further molybdenum containing compound; and d) at least one simple and/or complex soap thickener.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2006/009717 filed Oct. 7, 2006 which is hereby incorporated byreference in its entirety.

FIELD

The present invention relates to a lubricating grease which is intendedprimarily for use in constant velocity universal joints, especially balljoints or tripod joints, which are used in the drivelines of motorvehicles.

BACKGROUND

The motions of components within constant velocity joints (CVJ) arecomplex with a combination of rolling, sliding and spinning. When thejoints are under torque, the components are loaded together which cannot only cause wear on the contact surfaces of the components, but alsorolling contact fatigue and significant frictional forces between thesurfaces. The wear can result in failure of the joints and thefrictional forces can give rise to noise, vibration and harshness (NVH)in the driveline. NVH is normally “measured” by determining the axialforces generated in plunging type CVJ. Ideally the greases used inconstant velocity joints need not only to reduce wear, but also have tohave a low coefficient of friction to reduce the frictional forces andto reduce or prevent NVH.

Constant velocity joints also have sealing boots of elastomeric materialwhich are usually of bellows shape, one end being connected to the outerpart of the CVJ and the other end to the interconnecting or output shaftof the CVJ. The boot retains the grease in the joint and keeps out dirtand water.

Not only must the grease reduce wear and friction and prevent thepremature initiation of rolling contact fatigue in a CVJ, it must alsobe compatible with the elastomeric material of which the boot is made.Otherwise there is a degradation of the boot material which causespremature failure of the boot, allowing the escape of the grease andultimately failure of the CVJ. The two main types of material used forCVJ boots are polychloroprene rubber (CR) and thermoplastic elastomer(TPE), especially ether-ester block co-polymer thermoplastic elastomer(TPC-ET).

Typical CVJ greases have base oils which are blends of naphthenic(saturated rings) and paraffinic (straight and branched saturatedchains) mineral oils. Synthetic oils may also be added. It is known thatsaid base oils have a large influence on the deterioration (swelling orshrinking) of both boots made of CR and TPC-ET. Usual mineral andsynthetic base oils extract the plasticisers and other oil-solubleprotective agents from the boot materials. Paraffinic mineral oils andpoly-α-olefin (PAO) synthetic base oils diffuse very little intoespecially boots made of rubber material causing shrinkage, but on theother hand naphthenic mineral oils and synthetic esters diffuse intoboot materials and act as plasticisers and can cause swelling. Theexchange of plasticiser or plasticiser compositions for the naphthenicmineral oil can significantly reduce the performance, especially at lowtemperatures, and may cause the boot to fail by cold cracking,ultimately resulting in failure of the CVJ. If significant swelling orsoftening occurs, the maximum high speed capability of the boot isreduced due to the poor stability at speed and/or excessive radialexpansion.

In order to solve the aforesaid problems, U.S. Pat. No. 6,656,890 B1suggests a special base oil combination comprising 10 to 35% by weightof one or more poly-α-olefins, 3 to 15% by weight of one or moresynthetic organic esters, 20 to 30% by weight of one or more naphthenicoils, the remainder of the combination being one or more paraffinicoils, and, further, a lithium soap thickener, and a sulphur-freefriction modifier, that may be a organo-molybdenum complex, andmolybdenum dithiophosphate, and a zinc dialkyldithio-phosphate andfurther additives such as corrosion inhibitors, anti-oxidants, extremepressure additives, and tackiness agents. However, the frictioncoefficient and the wear of grease compositions according to U.S. Pat.No. 6,656,890 B1 as measured in SRV (abbreviation for the German wordsSchwingungen, Reibung, Verschleiβ) tests need to be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a is a graph of friction coefficient data for grease compositionembodiments of the present invention and comparison compositions thatlack the combination of a tri-nuclear molybdenum compound containingsulfur and a further molybdenum containing compound;

FIG. 1 b is a graph of wear data for grease composition embodiments ofthe present invention and comparison compositions that lack thecombination of a tri-nuclear molybdenum compound containing sulfur and afurther molybdenum containing compound;

FIG. 2 a is a graph of friction coefficient data for grease compositionembodiments of the present invention with varying amounts of atri-nuclear compound containing sulfur, and with varying amounts of afurther molybdneum containing molybdenum compound and/or a zincdithiophosphate compound;

FIG. 2 b is a graph of wear data for grease composition embodiments ofthe present invention with varying amounts of a tri-nuclear molybdenumcompound containing sulfur, and with varying amounts of a furthermolybdneum containing compound and/or a zinc dithiophosphate compound;

FIG. 3 is a graph of axial force data for grease compositions B1 and B2of FIGS. 2 a and 2 b;

FIG. 4 a is graph of welding load data for grease compositionembodiments of the present invention with varying amounts of an extrapressure agent; and

FIG. 4 b is a graph of friction coefficient data for grease compositionembodiments of the present invention with varying amounts of an extrapressure agent.

DETAILED DESCRIPTION

Thus, it is the object of the present invention to provide for a greasecomposition, primarily for use in constant velocity joints, which has agood compatibility with boots made of rubber or thermoplastic elastomer,and which also gives low wear and low friction in use in CVJ.

Said object of the present invention is solved by a grease compositionfor use in constant velocity joints comprising

-   -   a) a base oil composition;    -   b) at least one tri-nuclear molybdenum compound, preferable        0.25% by weight to 5% by weight, more preferable 0.3% by weight        to 3% by weight, referred to the total amount of the grease        composition, of the formula

MO₃S_(k)L_(n)Q_(z),

-   -   -   wherein L are independently selected ligands having organo            groups with a sufficient number of carbon atoms to render            the compound soluble or dispersible in the oil, n is from 1            to 4, k varies from 4 though 7, Q is selected from the group            of neutral electron donating compounds such as amines,            alcohols, phosphines, and ethers, and z ranges from 0 to 5            and includes non-stoichiometric values,

    -   c) at least one further molybdenum containing compound, and

    -   d) at least one simple and/or complex soap thickener.

The number of carbon atoms present in the tri-nuclear molybdenumcompound among all the ligands, organo groups is at least 21 carbonatoms, preferably at least 25, more preferably at least 30, and mostpreferably at least 35. Tri-nuclear molybdenum compounds usable in thepresent invention are disclosed in U.S. Pat. No. 6,172,013 B1, thedisclosure of which is incorporated in the present invention insofar byreference. The inventors of the present invention have found that thepresence of at least one tri-nuclear molybdenum compound and a furthermolybdenum containing compound according to claim 1 would significantlylower the friction coefficient as well as the wear when used in CVJ.

As a base oil composition according to the present invention, a base oilcomposition as disclosed in U.S. Pat. No. 6,656,890 B1, the disclosureof which is incorporated insofar herein by reference, may preferably beused. However, any further kind of base oil composition, especially ablend of mineral oils, a blend of synthetic oils or a blend of a mixtureof mineral and synthetic oils may be used. The base oil compositionshould preferably have a kinematic viscosity of between about 32 andabout 250 mm²/s at 40° C. and between about 5 and about 25 mm²/s at 100°C. The mineral oils preferably are selected from the group comprising atleast one naphthenic oil and/or at least one paraffinic oil. Thesynthetic oils usable in the present invention are selected from a groupcomprising at least one poly-α-olefin (PAO) and/or at least onesynthetic organic ester. The organic synthetic ester is preferably adi-carboxylic acid derivative having subgroups based on aliphaticalcohols. Preferably, the aliphatic alcohols have primary, straight orbranched carbon chains with 2 to 20 carbon atoms. Preferably, theorganic synthetic ester is selected from a group comprising sebacicacid-bis(2-ethylhexylester) (“dioctyl sebacate” (DOS)), adipicacid-bis-(2-ethylhexylester) (“dioctyl adipate” (DOA)), and/or azelaicacid-bis(2-ethylhexylester) (“dioctyl azelate (DOZ)).

If poly-α-olefin is present in the base oil composition, preferablypoly-α-olefins are selected having a viscosity in a range from about 2to about 40 centistokes at 100° C. Naphthenic oils selected for the baseoil compositions have preferably a viscosity in a range between about 20to about 180 mm²/s at 40° C., whereas if paraffinic oils were present inthe base oil composition, preferably the paraffinic oils have aviscosity in a range between about 25 to about 400 mm²/s at 40° C.

In an preferred embodiment of the present invention, the furthermolybdenum containing compound is selected from the group comprisingmolybdenum dithiocarbamates and/or molybdenum dithiophosphates. The atleast one molybdenum dithiophosphate (MoDTP) and/or molybdenumdithiocarbamate (MoDTC) is preferably present in the grease compositionaccording to the present invention in an amount in a range between about0.3% by weight to about 3% by weight, in each case referred to the totalamount of the grease composition. However, also any further molybdenumcontaining compound may be present in the grease composition accordingto the present invention as component c), of which organic molybdenumcompounds are preferred. The grease composition according to the presentinvention may contain one or more MoDTC and/or MoDTP, and especiallyalso mixtures thereof. The MoDTP according to the present invention isof the following general formula:

wherein X or Y represents S or 0 and each of R¹ to R⁴ inclusive may bethe same or different and each represents a primary (straight chain) orsecondary (branched chain) alkyl group having between 6 and 30 carbonatoms.

The MoDTC according to the present invention is of the following generalformula:

[(R⁵)(R⁶)N—CS—S]₂—Mo₂O_(m)S_(n)  (III)

wherein R⁵ and R⁶ each independently represents an alkyl group having 1to 24, preferably 3 to 18 carbon atoms; m ranges from 0 to 3 and nranges from 4 to 1, provided that m+n=4.

The addition of two molybdenum containing compounds, one of which is atri-molecular molybdenum compound containing sulphur (TNMoS), whereasthe further molybdenum containing compound is preferably at least one ofMoDTPs and/or MoDTCs lowers the friction coefficient and the wear ofCVJs in use significantly. Especially, the friction coefficient isdiminished by at least about 25% compared to grease compositionscontaining only at least one TNMoS.

The at least one simple and/or complex soap thickener according to thegrease composition claimed is preferably selected from the groupcomprising Lithium soaps and/or Calcium soaps.

In the sense of the present invention, a lithium soap or a calcium soapis a reaction product of at least one fatty acid with lithiumhydroxideor calciumhydroxide. Preferably, the thickener may be a simple lithiumor calcium soap formed from stearic acid, 12-hydroxy stearic acid,hydrogenated castor oil or from other similar fatty acids or mixturesthereof or methylesters of such acids. Alternatively, a lithium and/orcalcium complex soap may be used formed for example from a mixture oflong-chained fatty acids together with a complexing agent, for example aborate of one or more dicarboxylic acids. The use of complex lithiumand/or calcium soaps allows the grease composition according to thepresent invention to operate up to a temperature of about 180° C.,whereas with simple lithium and/or calcium soaps, the grease compositionwill only operate up to a temperature of about 120° C. However, mixturesof all of the aforesaid thickeners may also be used.

In a further embodiment of the present invention, the grease compositionfurther comprises at least one zinc compound additive, more preferably azinc compound additive in an amount of about 0.1% by weight to about 3%by weight, preferably about 0.3% by weight to about 2% by weight,referred to the total amount of the grease composition. The mostpreferred the zinc compound additive is selected from the groupcomprising at least one of zinc dithiophosphates (ZnDTP). The zincdithiophosphate is preferably selected from the group of zincdialkyldithiophosphate of the following general formula:

(R⁷O)(R⁸I)SP—S—Zn—S—PS(OR⁹)(OR¹⁰)  (IV)

wherein each of R⁷ to R¹⁰ inclusive may be the same or different andeach represents a primary or secondary alkyl group having 1 to 24,preferably 3 to 20, most preferably 3 to 5 carbon atoms. In particular,excellent effects can be expected if the substituants R⁷, R⁸, R⁹ and R¹⁰represent a combination of primary and secondary alkyl groups, eachhaving 3 to 8 carbon atoms.

By adding at least one zinc compound additive to the grease compositionaccording to the invention, the wear in CVJ is diminished furthersignificantly.

According to a further embodiment of the present invention, the greasecomposition further comprises an additive package selected from thegroup of agents comprising antioxidation agents, corrosion inhibitors,anti-wear agents, friction modifiers, and/or extreme pressure agents (EPagents).

The EP agent is preferably a metal-free, sulphurised fatty acid methylester agent with a viscosity of about 25 mm²/s at 40° C. being presentpreferably in an amount between about 0.1 to about 3% by weight,referred to the total amount of the grease composition. The totalsulphur amount of the EP agent preferably ranges from about 8 to about10% by weight and the active sulphur amount is about 1% by weight. SuchEP agents exhibit excellent effects with respect to the prevention ofseizure of CVJ. If the sulphur content exceeds the upper limit definedabove, it may promote the initiation of rolling contact fatigue and wearof the contacting metal components.

As an anti-oxidation agent, the grease composition of the presentinvention may comprise an amine, preferably an aromatic amine, morepreferably phenyl-α-naphthylamine or diphenylamine or derivativesthereof. The anti-oxidation agent is used to prevent deterioration ofthe grease composition associated with oxidation. The grease compositionaccording to the present invention may range between about 0.1 to about2% by weight, referred to the total amount to the grease composition, ofan anti-oxidant agent in order to inhibit the oxidation degradation ofthe base oil, as well as to lengthen the life of the grease composition,thus prolonging the life of the CVJ. Typically, the last operationbefore the assembly of CVJ is a wash to remove machining debris, and itis therefore necessary for the grease to absorb any traces of remainingwater and to prevent the water from causing corrosion and adverselyeffecting the performance of the CVJ, it is therefore necessary to add acorrosion inhibitor. As a corrosion inhibitor, the grease compositionaccording to the present invention may comprise at least one metal saltselected from the group consisting of metal salts of oxidised waxes,metal salts of petroleum sulphonates, especially prepared bysulphonating aromatic hydrocarbon components present in fractions oflubricating oils, and/or metal salts of alkyl aromatic sulphonates, suchas dinonylnaphtalene sulphonate, alkylbenzene suiphonic acids, oroverbased alkylbenzene sulphonic acids, Examples of the metal saltsinclude sodium salts, potassium salts, calcium salts, magnesium salts,zinc salts and quaternary ammonium salts, the calcium salts being mostpreferred. Calcium salts of oxidised waxes also ensure an excellenteffect.

Anti-wear agents according to the present invention prevent ametal-to-metal contact by adding film-forming compounds to protect thesurface either by physical absorption or chemical reaction.ZnDTP-compounds may also be used as anti-wear agents. As anticorrosionagents according to the present invention preferably calcium sulphonatesalts are used, preferably an amount between about 0.5 to about 3% byweight, referred to the total amount of the grease composition.

Traditional friction modifiers such as fatty acid amides and fatty aminephosphates have been used in greases and other lubricants for many years(see, e.g., Klamann, Dieter-“Lubricants”, Verlag Chemie GmbH 1983,chapter 9.6 as reference). Their role is to give the lubricant stablebut not necessarily low friction over a wide range of operatingconditions.

In a further preferred embodiment of the present invention, a greasecomposition comprises about 55% by weight to about 98% by weight of thebase oil composition, about 0.1% by weight to about 5% by weight of atleast one tri-nuclear molybdenum compound, about 0.3% by weight to about2% by weight of at least one further molybdenum compound, and about 1%by weight to about 25% by weight of at least one soap thickener, in eachcase referred to the total amount of the grease composition.

In a further preferred embodiment of the present invention, the amountof the tri-nuclear molybdenum compounds, molybdenum dithiophosphates,molybdenum dithiocarbamates, and/or zinc dithiophosphates present in thecomposition is in a range of between about 0.3% by weight to about 2% byweight, in each case referred to the total amount of the greasecomposition. Most preferably, the weight percentage added, referred tothe total amount of the grease composition, of the tri-nuclearmolybdenum compounds is essentially identical with the weight percent ofmolybdenum dithiophosphates, molybdenum dithiocarbamates, or zincdithiophosphates added, and is preferably about 0.4% by weight, about0.5% by weight, about 0.6% by weight and/or about 0.7% by weight, ineach case referred to the total amount of the grease composition.

Further, the grease composition according to the present invention has asliding friction coefficient of not more than 0.08, as measured with aSRV test, and is typically below 0.07.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to determine the effect of the lowering of the frictioncoefficient as well as the wear by the grease composition according tothe invention, SRV tests are carried out using an Optimol InstrumentsSRV tester. Flat disc lower specimen made of the 100Cr6 standard bearingsteel from Optimol Instruments Prüftechnik GmbH, Westendstrasse 125,Munich, properly cleaned using a solvent are prepared and contacted withthe grease composition to be examined. The SRV test is an industrystandard test and is especially relevant for the testing of greases forCVJ. The test consists of an upper ball specimen with a diameter of 10mm made from 100Cr6 bearing steel reciprocating under load on the flatdisc lower specimen indicated above. In tests for mimicking tripodjoints a frequency of 40 Hz with an applied load of 200 N were appliedfor 60 minutes (including running-in) at 80° c. The stroke was 1.5 mmand 3.0 mm, respectively. The friction coefficients obtained wererecorded on computer. For each grease, the reported value is an averageof four data at the end of tests in four runs (two runs at 1.5 mm strokeand two runs with 3.0 mm stroke). Wear is measured using a profilometerand a digital planimeter. By using the profilometer, a profile of thecross section in the middle of the worn surfaces can be obtained. Thearea (S) of this cross section can be measured by using the digitalplanimeter. The wear quantity is assessed by V=SI, where V is the volumeof the wear and I is the stroke. The wear rate (Wr) is obtained fromW_(r)=V/L [μm³/m], where L is the total sliding distance in the tests.For the running-in, it is started with an applied load of 50 N for 1minute under the above-specified conditions. Afterwards, the appliedload is increased for 30 seconds by 50 N up to 200 N.

Further, the axial forces generated by a plunging tripod joint atvarious articulation angles is measured in accordance with the followingmethod:

Axial Cyclic Force Generation Test

This test is for measurement of axial cycles force generated by adriveshaft assembly or plunging constant velocity joint under hightorque and low speed, similar to the take off shudder conditions in thevehicle. The driveshaft assembly with a plunging joint, is mounted on atest rig capable of applying rotation, torque and articulation to theconstant velocity joint. The test rig is equipped with a joint coolingsystem. A force transducer is fitted to the test rig and used to measurethe force along the rotation axis of the joint.

Before the test, a running-in procedure is applied as follows:

-   -   Grease distribution: ensure consistent lubrication conditions        under a torque of +100 Nm and speed of +200 rpm sweeping        sinusoidally at angles between 0 to 20 degree 4 cycles per        minute for 5 minutes    -   full stabilized axial force values under the conditions:

Torque (Nm) Speed (rpm) Angle (degree) Duration (hour) +300 +200sweeping sinusoidally at 0.5 +600 +200 angles between 0 to 20 1 −300−200 degree 4 cycles per minute 0.5 −600 −200 1

-   -   Warm-up: ensure stablised temperature and lubrication conditions        for joint which have already had a full running-in under a        torque of +300 Nm and speed of +200 rpm sweeping sinusoidally at        angles between 0 to 20 degree 4 cycles per minute for 15 minutes    -   Grease running-in: to run-in greases for joints which have        already had a full running-in under the conditions:

Torque (Nm) Speed (rpm) Angle (degree) Duration (hour) +300 +200sweeping sinusoidally at 0.5 +600 +200 angles between 0 to 20 1 −300−200 degree 4 cycles per minute 0.5 −600 −200 1 Other conditions: JointAngle: 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 degree applied torque+/−600 Nm torque with +/−200 rpm speed

The load carrying capacity of a CVJ grease is an important property thatdefines the resistance of the grease to adhesive wear and scuffing. Forgreases it is defined as the welding load in Newtons as measured by a 4ball EP test according to the IP-239 standard published by the EnergyInstitute, London, UK.

The following substances are used in the examined grease compositions:

Base Oil Composition

The base oil compositions used have a kinematic viscosity of betweenabout 32 and about 250 mm²/s at about 40° C. and between about 5 andabout 25 mm²/s at 40° C. Two base oil blends are used in this invention.The base oil blend A is a mixture of one or more naphthenic oils in arange between about 10 to about 60% by weight, one or more paraffinicoils in a range between about 30 to about 80% by weight and one or morepolyalpha-olefins (PAO) in a range between about 5 to about 40% byweight referred to the total amount of the oil mixture. Oil blend A doesnot contain an organic synthetic ester, whereas oil blend 8 contains DOSin a range between about 2 to about 10% by weight referred to a totalamount of the oil mixture.

The naphthenic oils are selected with a range of viscosity between about20 to about 180 mm²/s at 40° C., paraffinic oils between about 25 toabout 400 mm²/s at 40° C., and PAO between about 6 and about 40 mm²/s at100° C.

Tri-Molecular Molybdenum Compound (TNMoS)

The tri-molecular molybdenum compound used in the grease compositionsaccording to the present invention is a sulphur-containing tri-nuclearmolybdenum compound obtainable under the trade name C94558 by InfineumInternational Ltd., UK. Its structure is defined in U.S. Pat. No.6,172,013 B4.

Further Molybdenum Containing Compounds for Comparative Examples

A molybdenum dithophosphate (MoDTP) sold under the commercial nameSakuralube 300 (S-300) by Asahi Denka Co. Ltd., Japan, with the chemicalformula 2-Ethylhexyl molybdenum dithiophosphate, diluted with mineraloil, is used. Further, a molybdenum dithiocarbamate (MoDTC) sold underthe trade name Sakuralube 600 (3-600) in the solid state, produced byAsahi Denka Co. Limited, Japan, being in accordance with formula III, isused.

Zinc Compound Additive

As zinc compound additives, ZnDTP, sold by Infineum International Ltd.,UK under the trade name Paranox-15, is used, being a zincdialkyldithiophosphate with primary and secondary allyl groups,preferably diluted with mineral oil.

Thickener

As a lithium soap (Li soap), a reaction product supplied by BrugarolasS.A., Spain, using fatty acid with lithiumhydroxide is used. Further, acalcium complex soap (Calcium complex soap) being a reaction product ofcalcium hydroxide with two carboxylic acids, one with a short carbonchain length of 2 to 5 carbon atoms and one with a long carbon chainlength of 16 to 20 carbon atoms in which the short to long chain ratiois between 1:2 and 1:5, is used.

Additives

As an anti-oxidant agent (anti-oxidant), a diphenylamine with butyland/or octyl-groups is used, supplied by Ciba Specialty Chemicals,Switzerland under the trade name L-57 (Irganox L57). As an EP agent (EPagent 1), a sulphurised organic compound (fatty acid methylester) soldunder the trade name Anglamol 33 by The Lubrizol Corporation, OH; U.S.A.(EP agent 1), or sold under the trade name DeoAdd MD 10 by DOG DeutscheOelfabrik Gesellschaft für chemische Erzeugnisse mbH und Co, Hamburg,Germany (“EP additive” in the examples) is used. Another example of anEP agent is a grease with calcium sulphonate thickeners, as produced byBrugarolas S.A., Spain, under the trade name Ca-S Grease (Ca-S grease).

As a corrosion inhibitor, a calcium salt ofdinonyl-naphthalensulphonate, distributed for example by KingIndustries, Norwalk, Conn., U.S.A., under the trade name NaSul 729 (Casulphonate) is used.

First, the advantages of the grease composition according to theinvention were examined by comparing the friction coefficient and wearof the same with grease compositions containing no TNMoS compound and nofurther molybdenum containing compound, or grease compositionscontaining only a TNMoS compound. Seven different grease compositionswere produced, as listed in the following table:

TABLE 1 Grease Composition Example Example Example Example ExampleExample Example [wt %] A1 A2 A3 A4 A5 A6 A7 TNMoS 0.5 1.5 1.0 2.0 2.0ZnDTP 0.5 1.0 0.5 1.0 1.0 MoDTP 0.5 1.0 1.0 0.5 1.0 MoDTC 0.5 0.5Anti-oxidant 0.25 0.25 0.25 0.25 0.25 0.25 0.25 oil blend A 81.75 80.7581.75 80.75 80.75 81.75 82.75 Calcium complex soap 16 16 16 16 16 16 16

The results from the SRV-measurement of the friction coefficient and thewear of examples A1 to A7 may be derived from FIG. 1. Example A7contains neither a TNMoS compound nor a further molybdenum containingcompound, whereas example A3 does not contain any further molybdenumcontaining compound. In contrast thereto, example A6 contains a furthermolybdenum containing compound, but no TNMoS compound. Thus, inaccordance with the present invention are only examples A1, A2, A4 andA5. One may clearly derive from FIG. 1( a) that the friction coefficientis significantly decreased in the grease compositions according to thepresent invention when compared to grease compositions not in accordancewith the present invention, and that the friction coefficient is below0.08. Further, the wear (see FIG. 1( b)) of the grease compositions A1,A2, A4, and A5 is either not measurable, or lower than in the greasecompositions being not in accordance with the present invention.

In a further series of tests, 8 grease compositions in accordance withthe present invention were prepared containing different concentrationseither of the TNMoS compound or the further molybdenum containingcompounds (MoDTP and MoDTC). The grease compositions are listed in Table2.

TABLE 2 Grease Composition Example Example Example Example ExampleExample Example Example [wt %] B1 B2 B3 B4 B5 B6 B7 B8 TNMoS 0.5 1.5 0.10.3 1.0 0.5 0.5 0.5 ZnDTP 0.5 0.5 0.5 0.5 1.0 0.5 0.5 MoDTP 0.5 1.0 0.50.5 0.5 0.5 1.0 0.5 MoDTC 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 Anti-oxidant0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 oil blend B 91.5 90.5 91.9 91.7 91.091.0 91.0 91.0 Li soap 6 6 6 6 6 6 6 6Examples B1 and B2 are similar to examples A1 and A2. The results fromSRV tests with respect to the friction coefficient and wear will be seenfrom FIG. 2.

As may be taken from the values for the friction coefficient from FIG.2, the friction coefficient of grease compositions is for all examplesB1 to B8 around or below 0.08. Since the concentration of the TNMoScompound is changed from 0.3% by weight to 1.5% by weight, referred tothe total amount of the grease composition, it appears that in a rangefrom about 0.25% by weight to about 2% by weight at least one TNMoScompound should be present in the grease composition in accordance withthe present invention. The lowest friction coefficients were obtained byadding about 0.5% by weight of at least one TNMoS compound to the greasecomposition. The addition of MoDTPs and/or MoDTCs being present in arange from about 0.5% by weight to about 1% by weight, referred to thetotal amount of the grease composition, resulted in no significantchange of the friction coefficient.

Further, from FIG. 2 it may be taken that the addition of at least oneZnDTP in an amount of at least about 0.5% by weight to 1% by weight,referred to the total amount of the grease composition, is advantageous,because example B2 without any ZnDTP additive shows a higher frictioncoefficient when compared to examples B1 and B3 to B8.

With respect to the wear measurements, examples B1 and B3 show nomeasurable wear, whereas the addition of about 1% by weight of MoDTPsand/or MoDTCs resulted in a higher value for the wear, as may be takenfrom examples B2, B7 and B8.

The slightly different values for the friction coefficient and the wearof examples A1 and A2 when compared with examples B1 and B2 is due tothe use of a different base oil composition and the use of a lithiumsoap thickener instead of a calcium complex soap thickener as used inexamples A1 to A7. It appears that the addition of a calcium complexsoap thickener is slightly more preferable than the addition of thelithium soap thickener with respect to the friction coefficient and thewear.

Further, the axial forces of grease compositions in accordance withexamples B1 and B2 were measured, and are graphically represented inFIG. 3.

The axial force should be lower than a requirement set by the applicant.One may derive from FIG. 3 that the example B1 gives values for theaxial force being below the values for the requirement whereas at anglesaround 13°, a grease composition in accordance with example B2 wouldlead to axial forces being higher than the requirement. Thus, greasecomposition B1 containing in addition the ZnDTP agent is most preferred.

In a third test series, the effect of the addition of other componentson grease compositions in accordance with the present invention wasexamined by preparing grease compositions in accordance with Table 3.

TABLE 3 Grease Composition Example Example Example Example ExampleExample [wt %] C1 C2 C3 C4 C5 C6 TNMoS 0.5 0.5 0.5 0.5 0.5 0.5 ZnDTP 0.50.5 0.5 0.5 0.5 0.5 MoDTP 0.5 0.5 0.5 0.5 0.5 0.5 MoDTC 0.5 0.5 0.5 0.50.5 0.5 EP additive 1 0.5 EP additive 2 0.5 anti corrosion 2.0 Calcium 5complex soap Ca—S grease 3 Anti-oxidant 0.5 0.5 0.5 0.5 0.5 0.5 oilblend B 91.5 91.0 91.0 89.5 86.5 88.5 Li soap 6.0 6.0 6.0 6.0 6.0 6.0

The results from SRV tests with respect to the friction coefficient aswell as the measurement of the welding load with respect to examples C1to C6 are shown in FIG. 4. The grease composition of example C1 isidentical to example B1.

One may derive from FIG. 4 that the addition of a higher amount of an EPagent is preferred, as may be taken from the high value for the weldingload especially for example C2. However, the friction coefficient isslightly increased by the addition of EP agents. The addition of acalcium complex grease in addition to a lithium soap grease leads to afurther lowering of the friction coefficient, as may be see in exampleC5. However, the welding load is only slightly increased with respect toexample C1. Further, the addition of a calcium sulphonate grease (Ca-Sgrease) increases the value for the welding load and decreases thefriction coefficient of the grease composition, as may be taken fromexample C6. The addition of the corrosion inhibitor does notsignificantly influence the friction coefficient, however, the value forthe welding load is significantly increased, as may be derived whencomparing example C1 with example C4.

Thus, the addition of an EP agent in an amount in a range of about 0.1%by weight to about 1.0% by weight, as well as the addition of ananti-corrosion agent in an amount of between about 0.3% by weight toabout 3% by weight, and the addition of a calcium sulphonate grease inan amount of between about 0.5% by weight to about 15% by weight, ineach case referred to the total amount of the grease composition, ispreferred.

In summary, the grease composition according to the present inventionhas an advantageous significant influence on the friction coefficientand wear as well as on the welding load and the axial forces, leading tolower wear and lower friction in CVJ, and thus are able to reduce orprevent noise, vibration and harshness (NVH) in the driveline.

1. A grease composition for use in constant velocity joints comprising:a) a base oil composition; b) at least one tri-nuclear molybdenumcompound of the formulaMo₃S_(k)L_(n)Q_(z),  wherein L are independently selected ligands havingorgano groups with a sufficient number of carbon atoms to render thecompound soluble or dispersible in the oil, n is from 1 to 4, k variesfrom 4 though 7, Q is selected from the group of neutral electrondonating compounds consisting of amines, alcohols, phosphines, andethers, and z ranges from 0 to 5 and includes non-stoichiometric values.c) at least one further molybdenum containing compound; and d) at leastone selected from the group consisting of a simple soap thickener and acomplex soap thickener.
 2. A grease composition according to claim 1,characterised in that the further molybdenum containing compound is atleast one selected from the group consisting of molybdenumdithiocarbamates and molybdenum dithiophosphates.
 3. A greasecomposition according to claim 1, comprising as a further molybdenumcompound 0.3% by weight to 3% by weight of at least one selected fromthe group consisting of molybdenum dithiophosphate (MoDTP) andmolybdenum dithiocarbamate (MoDTC), in each case referred to the totalamount of the grease composition.
 4. A grease composition according toclaim 1, characterised in that the soap thickener is at least oneselected from the group consisting of Lithium soaps and Calcium soaps.5. A grease composition according to claim 1, further comprising atleast one zinc dithiophosphate additive (ZnDTP).
 6. A grease compositionaccording to claim 1, further comprising 0.3% by weight to 3% by weightof at least one zinc dithiophosphate additive (ZnDTP), referred to thetotal amount of the grease composition.
 7. A grease compositionaccording to claim 1, further comprising an additive package includingat least one selected from the group consisting of anti-oxidationagents, corrosion inhibitors, anti-wear agents, friction modifiers andextreme pressure agents (EP agents).
 8. A grease composition accordingto claim 1, comprising 50% by weight to 98% by weight of the base oilcomposition, 0.1% by weight to 5% by weight of at least one tri-nuclearmolybdenum compound, 0.3% by weight to 2% by weight of at least onefurther molybdenum compound, and 1% by weight to 25% by weight of atleast one soap thickener, in each case referred to the total amount ofthe grease composition.
 9. A grease composition according to claim 1,characterised in that the amount of the tri-nuclear molybdenum compoundspresent in the composition is in a range of between 0.3% by weight to 3%by weight, in each case referred to the total amount of the greasecomposition.
 10. A grease composition according to claim 1,characterised in that the weight percent added, referred to the totalamount of the grease composition, of tri-nuclear molybdenum compounds isessentially identical with the weight percent of one selected from thegroup consisting of molybdenum dithiophosphates, molybdenumdithiocarbamates, or zinc dithiophosphates added.
 11. A greasecomposition according to claim 1, further comprising an addition of atleast one selected from the group consisting of Ca-sulphonate grease inan amount from 0.1% by weight to 10% by weight and at least one sulphurcontaining extreme pressure agent in an amount from 0.1% by weight to 3%by weight in each case referred to the total amount of the greasecomposition.
 12. A grease composition according to claim 1,characterised in that the sliding friction coefficient of saidcomposition is at most 0.8.